U.S. officials say President Barack Obama has nominated Marine Corps General Joseph Dunford, a commander in both the Afghan and Iraq wars, as the new chairman of the Joint Chiefs of Staff.

Dunford, 59, will replace U.S. Army General Martin Dempsey, who is expected to step down in September as the top U.S. military officer. Dunford's pick is widely expected to win swift Senate confirmation.

Before becoming the top commadner of the U.S. Marine Corps in 2014, Dunford led U.S. and international forces in Afghanistan as they handed over greater responsibility for security to Afghan government troops.

He earned the nickname "Fighting Joe" on the battlefields of Iraq, where he helped lead forces during the U.S. invasion in 2003.

Obama also nominated U.S. Air Force General Paul Selva, currently the commander of the U.S. Transportation Command, as the vice chairman of the Joint Chiefs of Staff.